1. Field of the Invention
The present invention relates to a method of performing high-efficiency machining by high-density radical reaction using a rotating electrode and a device for performing the method, and more particularly to a method of performing high-efficiency machining by high-density radical reaction using a rotating electrode, a device for performing the method and a rotating electrode used therefor, which is capable of machining with a high accuracy and a high efficiency without introducing a defect or a heat-affected layer into a semiconductor such as silicon monocrystal, a conductor, or an insulator such as glass or ceramics.
2. Description of the Related Art
Up to now, in cutting silicon monocrystal, there has been used, for example, a dicing machining method by a diamond wheel. Since this machining principle uses brittle destroy due to a fine crack, the machined surface is not crystallographically controlled, and a deep damage is always given to the machined surface to the degree of the thickness of the finished machining. In the case of manufacturing a semiconductor device using a wafer thus cut, a yield is poor, and its electrical performance is deteriorated. Also, the machining principle is one factor for measuring the limit of the integrated degree. This fact is applicable to machining of all of a variety of functional materials.
Under the circumstances, as disclosed in Japanese Patent Unexamined Publication No. Hei 1-125829 (U.S. Pat. No. 4,960,495), there has been proposed a non-strain precision machining method (plasma CVM method) in which the neutral radical of a reactive gas caused by high-density plasma generated by an electrode to which a high frequency is applied is supplied to a machined surface of a workpiece, and volatile material generated by radical reaction of the neutral radical with atoms or molecules constituting the machined surface is gasified so as to be removed, thereby being capable of performing machining with a high accuracy without introducing a defect or a heat-affected layer into a semiconductor such as silicon monocrystal, a conductor, or an insulator such as glass or ceramics.
In this specification, "CVM" is an abbreviation of "chemical vaporization machining".
In other words, the CVM is a method in which a workpiece and an electrode are disposed in an atmospheric gas containing a reaction gas, and a high-frequency voltage is applied between the workpiece and the electrode, to thereby produce the neutral radical based on the reaction gas in the vicinity of the electrode. In this situation, in the case where the machining electrode is formed of a wire electrode, the workpiece can be subjected to cutting machining or grooving machining; in the case where the machining electrode is formed of a planer electrode, the workpiece can be subjected to smoothing machining or specular machining; and in the case where the machining electrode is formed of a complicatedly shaped electrode, the workpiece can be subjected to transfer machining by which the shaped of the electrode is transferred to the workpiece.
In the case of cutting the workpiece, a structure using the wire electrode is effective. However, in the cutting machining using a normal wire electrode, the reaction gas cannot be sufficiently supplied into the cut groove which is formed during its process, and an electric power supplied to the electrode is low. Also, in the specular machining using the planar electrode having a large-area smooth surface, the reaction gas cannot be sufficiently supplied to the center of a machining gap, to thereby lower the density of the neutral radical on its portion. As a result, in case of the cutting machining, the machining speed is lowered with the progress of the machining, and in case of the specular machining, a difference in machining rate between the peripheral portion and the central portion of the electrode causes the nonuniformity of the amount of machining.
For that reason, the present inventor(s) have proposed a cutting method using a flat gas supply nozzle which is capable of being inserted into the machining groove (Japanese Patent Unexamined Publication No. Hei 1-162523), a machining method in which a gas supply hole is defined in a support body that holds the machining electrode (Japanese Patent Unexamined Publication No. Hei 4-337635, Japanese Patent Unexamined Publication No. Hei 5-96500, Japanese Patent Unexamined Publication No. Hei 6-168924), a machining method in which a gas supply means is provided in a machining electrode per se, and a reaction gas is forcedly supplied to a machining gap between the machining electrode and the workpiece (Japanese Patent Unexamined Publication No. Hei 4-246184, Japanese Patent Unexamined Publication No. Hei 6-85059), to thereby achieve a maximum machining rate of several tens .mu.m/m. This machining rate remarkably exceeds the common sense of the conventional plasma etching. However, it is insufficient for cut-machining the workpiece which is high in thickness and polish-machining a large area of the workpiece.
Since the machining rate has a close connection with the density of the neutral radical in the vicinity of the machining progress portion of the workpiece, that is, the density of the reaction gas and the making power for generating the neutral radical, it is presumed that the causes by which the machining rate could not be remarkably improved even in any conventional methods are that the supply of a reaction gas and the exhaust of used gas are insufficient, and that the limit value of the making power is low. It is presumed that the reason that the supply of the reaction gas and the exhaust of the used gas are insufficient in the plasma CVM of the present invention is that since the pressure of the gas atmosphere is very high to the degree of 1 atmospheric pressure or higher, and the machining gap is very narrow to the degree of 10 to 200 .mu.m, the viscous resistance of gas is very low. Also, the cause that the limit value of the making power is low is that the concentrated portion of the electric field of the machining electrode is heated, thereby being thermally damaged. For example, in case of conducting the cut-machining using the wire electrode under the gas atmosphere of 1 atmospheric pressure, the limit concentration of the reaction gas (SF.sub.6) is 1 to several %, and the limit making power is about 40 W/cm, by which the machining rate achieved is 20 to 30 .mu.m/sec. Moreover, in the case of ejecting the reaction gas from a gas supply nozzle or a gas supply hole, the distribution of density of the reaction gas is generated with the defect that the amount of machining is partially different, thereby not obtaining really uniformly machined surface.